A well known type of fire detection system using a sensor tube is illustrated in Lindberg Pat. No. 3,277,860 which uses a capillary sensor tube in which is encapsulated a pressurized gas which is released when heated. The rise in pressure actuates an electro-mechanical transducer which signals a fire alarm. Another type of fire related system is illustrated in Wacker Pat. No. 868,307 patented Oct. 15, 1907 where an elongated liquid filled sensor tube when heated by the presence of, for example, a nearby fire or rise in temperature operates on a diaphragm to turn on a water valve to extinguish the fire. Here a coiled thermostat is filled with a "confined expandable liquid such as mineral oil . . . " which when heated would actuate the diaphragm.
In the case of the Lindberg type sensor tube, it is relatively costly and may not be able to operate at the lower fire and hot gas temperatures found in some applications. Thus the liquid filled sensor tube in this respect is preferred. However, liquid filled tubes have difficulty with the normal expansion of the liquid under, for example, an increase in ambient temperature so that a false alarm is not caused. A application, Ser. No. 08/119,731 and assigned to the present assignee, in the name of Robert A. Fellows et al, now Pat. No. 5,458,202, does show a liquid filled fire related system but here the increase in pressure actuates a penetrator which releases pressurized fire extinguishant; because of the pressure thresholds involved, this is a relatively simple application of a liquid filled sensor tube where the expansion of the liquid under ambient temperature increase is a second order effect.